Use of Mixtures of Monocarboxylic Acids and Polycyclic Hydrocarbon Compounds for Improving the Storage Stability of Fuel Additive Concentrates

ABSTRACT

The use of mixtures of
     (A) aliphatic saturated or unsaturated monocarboxylic acids having from 12 to 24 carbon atoms or their dimerization or trimerization products, or their ammonium salts, amides, esters or nitrites, and   (B) polycyclic hydrocarbon compounds which are obtainable from distillation residues of natural oils which have been extracted from tree resins
 
for improving the storage stability of fuel additive concentrates which comprise at least one detergent and at least one cetane number improver, the mixtures of components (A) and (B) being used in a concentration of from 0.7 to 20% by weight based on the total amount of the fuel additive concentrate.

The present invention relates to the use of mixtures of aliphaticsaturated or unsaturated relatively long-chain monocarboxylic acids orderivatives thereof and polycyclic hydrocarbon compounds in a specificconcentration range for improving the storage stability of fuel additiveconcentrates which comprise at least one detergent and at least onecetane number improver. The invention further relates to a fuel additiveconcentrate which comprises detergents based on succinic anhydride,cetane number improvers and the abovementioned mixtures in specificratios.

After they have been produced, and before they are mixed into the fuelsin the refineries, fuel additive concentrates typically reside for along period in transport and storage vessels. This residence time may befrom a few weeks up to months. In the course of this, the fuel additiveconcentrates frequently tend to cloudiness, separation of the componentsand in some cases even to precipitation.

U.S. Pat. No. 5,591,237 (1) discloses that the storage stability of fueladditive concentrates which comprise detergents based on succinicanhydride, especially polyisobutenylsuccinimides, and cetane numberimprovers can be improved by adding nitric acid, hydrochloric acid oraliphatic monocarboxylic acids in an amount of from 1500 to 10 000 ppm.In the examples of (1), among other compounds, oleic acid in aconcentration of 6000 ppm and hydrochloric acid in a concentration of 10000 ppm in the concentrate are demonstrated to be effective improvers ofstorage stability.

EP-A 890 631 (2) describes an additive composition which comprises anashless detergent based on an acylated nitrogen compound, for example apolyisobutenylsuccinimide, and a relatively long-chain carboxylic acidor an ester thereof, and brings about improved lubricity of fuel oilsand better solubility in the fuel oils.

WO 98/04656 (3) describes the use of a fuel additive composed ofaliphatic saturated or unsaturated relatively long-chain monocarboxylicacids or derivatives thereof and polycyclic hydrocarbon compounds whichare obtained in particular from tall oil for improving the improvementin the lubrication properties of diesel fuels with low sulfur content.

It was an object of the present invention to further improve the storagestability of fuel additive concentrates which comprise detergents andcetane number improvers.

Accordingly, we have found the use of mixtures of

-   (A) aliphatic saturated or unsaturated monocarboxylic acids having    from 12 to 24 carbon atoms or their dimerization or trimerization    products, which may be present as free carboxylic acids and/or in    the form of ammonium salts, amides, esters and/or nitriles, and-   (B) polycyclic hydrocarbon compounds which are obtainable from    distillation residues of natural oils which have been extracted from    tree resins

for improving the storage stability of fuel additive concentrates whichcomprise at least one detergent and at least one cetane number improver,the mixtures of components (A) and (B) being used in a concentration offrom 0.7 to 20% by weight based on the total amount of the fuel additiveconcentrate.

Component (A) in the mixtures mentioned comprises preferably aliphaticsaturated or unsaturated monocarboxylic acids having from 14 to 20carbon atoms, in particular from 16 to 18 carbon atoms. Thesemonocarboxylic acids are generally linear. For component (A), usefulmonocarboxylic acids are in particular naturally occurring fatty acids,in particular those having from 14 to 20 carbon atoms, in particularfrom 16 to 18 carbon atoms. Typical representatives of suchmonocarboxylic acids or fatty acids are lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acidand elaidic acid. Component (A) may consist only of one suchmonocarboxylic acid or fatty acid or preferably of a mixture of two ormore such monocarboxylic acids or fatty acids. Naturally occurring fattyacids, as obtained, for example, from rapeseed oil, soya oil or talloil, are generally mixtures of a plurality of such monocarboxylic acids.

Component (B), whose natural origin is tree resins, in particularconifer resins from pines or spruces, is formed from one or preferablymore so-called resin acids. Resin acids are carboxyl-containingpolycyclic hydrocarbon compounds. They include, as the most importantrepresentatives, abietic acid, dehydroabietic acid, dihydroabietic acid,tetrahydroabietic acid, neoabietic acid, palustric acid, pimaric acid,isopimaric acid and levopimaric acid. These resin acids may partly alsobe present in oxidized form as so-called oxy acids.

In a preferred embodiment, components (A) and (B) are used in themixtures mentioned in a weight ratio of from 65:35 to 99.9:0.1,especially from 90:10 to 99.9:01, in particular from 97:3 to 99.9:0.1.

Particularly suitable mixtures of components (A) and (B) are tall oilfatty acid and dimerized tall oil fatty acid. Tall oil fatty acid isprepared from tall oil which is obtained by digestion of resin-rich woodtypes, in particular from spruce or pinewood. Tall oil fatty acid is amixture of fatty acids in which the C₁₈-unsaturated monocarboxylicacids, in particular oleic acid, linoleic acid and conjugated C₁₈ fattyacids, and also 5,9,12-octadecatrienoic acid predominate, resin acidsand, if appropriate, oxy acids (i.e. oxidized fatty acids and resinacids). Resin acid forms so-called tall resin in which abietic acid,dehydroabietic acid and palustric acid predominant and small fractionsof dihydroabietic acid, neoabietic acid, pimaric acid and isopimaricacid are detectable in addition to further resin acids. In the best talloil fatty acid quality, the fatty acid fraction is at least 97% byweight and the tall resin fraction up to 3% by weight.

The recovery of tall oil fatty acid and of resin acids from tree resinsby digestion, extraction and distillation processes is known to thoseskilled in the art and therefore need not be explained in detail here.

In dimerized tall oil fatty acid, the fatty acid component (A) ispresent in dimerized form. Dimerizations and trimerizations ofmonocarboxylic acids or fatty acids can be carried out by the processescustomary for this purpose and are known in principle to those skilledin the art.

The monocarboxylic acids or fatty acids and their dimerization ortrimerization products of component (A) may be present as freecarboxylic acids and/or as ammonium salts, for example as NH₄ salts orsubstituted ammonium salts, such as mono-, di-, tri- ortetramethylammonium salts, and/or in the form of amides, esters and/ornitriles. Typical amide structures have the —CO—NH₂, —CO—NH-alkyl or—CO—N(alkyl)₂ moieties, where “alkyl” here in particular represents C₁-to C₄-alkyl radicals such as methyl or ethyl. Ester structures typicallyinclude C₁- to C₄-alkanol ester radicals such as methyl or ethyl esterradicals.

The fuel additive concentrates mentioned may in principle be used toadditize any fuels or fuel oils. However, they are suitable inparticular for additizing diesel fuels (middle distillate fuels). Dieselfuels (middle distillate fuels) are typically crude oil raffinates whichgenerally have a boiling range from 100 to 400° C. These are usuallydistillates having a 95% point up to 360° C. or even higher. They mayalso be so-called “ultra-low sulfur diesel” or “city diesel”,characterized by a 95% point of, for example, not more than 345° C. anda sulfur content of not more than 0.005% by weight, or by a 95% pointof, for example, 285° C. and a sulfur content of not more than 0.001% byweight. In addition to the diesel fuels obtainable by refining, whosemain constituents are relatively long-chain paraffins, suitable dieselfuels are those which are obtainable by cool gasification or gasliquefaction [“gas-to-liquid” (GTL) fuels]. Also suitable are mixturesof the aforementioned diesel fuels with renewable fuels such asbiodiesel or bioethanol. Of particular interest at present are dieselfuels with a low sulfur content, i.e. with a sulfur content of less than0.05% by weight, preferably of less than 0.02% by weight, in particularof less than 0.005% by weight and especially of less than 0.001% byweight of sulfur. Diesel fuels may also comprise water, for example inan amount of up to 20% by weight, for example in the form ofdiesel-water microemulsions or as so-called “white diesel”.

Detergents (detergent additives) refer typically to depositioninhibitors for fuels, here in particular diesel fuels. The detergentsare preferably amphiphilic substances which have at least onehydrophobic hydrocarbon radical having a number-average molecular weight(M_(n)) of from 85 to 20 000, especially from 300 to 5000, in particularfrom 500 to 2500, and at least one polar moiety.

In a preferred embodiment, the mixture of components (A) and (B) is usedto improve the storage stability of fuel additive concentrates which, inaddition to at least one cetane number improver, comprise at least onedetergent having moieties which are derived from succinic anhydride andhave hydroxyl and/or amino and/or amido and/or imido groups.

This detergent having moieties which are derived from succinic anhydrideand have hydroxyl and/or amino and/or amido and/or imido groups is morepreferably a polyisobutenyl-substituted succinimide.

Additives comprising moieties which are derived from succinic anhydrideand have hydroxyl and/or amino and/or amido and/or imido groups arepreferably corresponding derivatives of polyisobutenylsuccinic anhydridewhich are obtainable by reacting conventional or highly reactivepolyisobutene having M_(n)=from 300 to 5000, in particular havingM_(n)=from 500 to 2500, with maleic anhydride by a thermal route or viathe chlorinated polyisobutene. Of particular interest in this contextare derivatives with aliphatic polyamines such as ethylenediamine,diethylenetriamine, triethylenetetramine or tetraethylenepentamine. Themoieties with hydroxyl and/or amino and/or amido and/or imido groupsare, for example, carboxylic acid groups, acid amides, acid amides ofdi- or polyamines which, in addition to the amide function, also havefree amine groups, succinic acid derivatives having an acid and an amidefunction, carboximides with monoamines, carboximides with di- orpolyamines which, in addition to the imide function, also have freeamine groups, and diimides which are formed by the reaction of di- orpolyamines with two succinic acid derivatives. Such fuel additives aredescribed in particular in U.S. Pat. No. 4,849,572.

The cetane number improvers (ignition or combustion improvers) used aretypically organic nitrates. Such organic nitrates are in particularnitrate esters of unsubstituted or substituted aliphatic orcycloaliphatic alcohols, usually having up to about 10, in particularhaving from 2 to 10 carbon atoms. The alkyl group in these nitrateesters may be linear or branched, saturated or unsaturated. Typicalexamples of such nitrate esters are methyl nitrate, ethyl nitrate,n-propyl nitrate, isopropyl nitrate, allyl nitrate, n-butyl nitrate,isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, n-amyl nitrate,isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, tert-amyl nitrate,n-hexyl nitrate, n-heptyl nitrate, sec-heptyl nitrate, n-octyl nitrate,2-ethylhexyl nitrate, sec-octyl nitrate, n-nonyl nitrate, n-decylnitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexylnitrate and isopropylcyclohexyl nitrate. Also suitable are, for example,nitrate esters of alkoxy-substituted aliphatic alcohols such as2-ethoxyethyl nitrate, 2-(2-ethoxyethoxy)ethyl nitrate, 1-methoxypropylnitrate or 4-ethoxybutyl nitrate. Also suitable are diol nitrates suchas 1,6-hexamethylene dinitrate. Among the cetane number improver classesmentioned, preference is given to primary amyl nitrates, primary hexylnitrates, octyl nitrates and mixtures thereof.

In a preferred embodiment, the mixture of components (A) and (B) is usedto improve the storage stability of fuel additive concentrates which, inaddition to at least one detergent, comprise 2-ethylhexyl nitrate as acetane number improver. In this case, 2-ethylhexyl nitrate may bepresent as the sole cetane number improver or in a mixture with othercetane number improvers.

The fuel additive concentrates mentioned, which are suitable inparticular for additizing diesel fuels (middle distillate fuels) may, inaddition to the detergent component and the cetane number improvercomponent, include further customary additive components, for examplecorrosion inhibitors, demulsifiers, antifoams, antioxidants andstabilizers, antistats, lubricity improvers, dyes (markers) and/orsolvents and diluents.

In the context of the present invention, the mixture of carboxylic acids(A) and the polycyclic hydrocarbon compounds (B) is used in amounts offrom 0.7 to 20% by weight, especially from 1.1 to 15% by weight, inparticular from 1.5 to 10% by weight, more preferably from 3 to 8% byweight, based in each case on the total amount of the fuel additiveconcentrate. The use concentration of the mixture of (A) and (B) is acritical parameter, since it has been found that the dosage rate of 6000ppm (corresponding to 0.6% by weight) recommended in (1) formonocarboxylic acids (by way of example for oleic acid) does not bringabout sufficient storage stability for the fuel additive concentrates.The additional amount of the mixture of (A) and (B) in the presentinvention compared to the teaching of (1) also exhibits additionalpositive effects in the use of the fuel additive concentrates; inparticular, the lubricity of low-sulfur diesel fuel additized therewithis simultaneously improved.

Since some of the fuel additive concentrates mentioned constitute novelsubstance mixtures, the present invention also provides a fuel additiveconcentrate which, based in each case on the total amount of the fueladditive concentrate, comprises

-   (a) from 0.5 to 60% by weight, especially from 10 to 45% by weight,    in particular from 20 to 35% by weight, of one or more detergents    which have moieties which are derived from succinic anhydride and    have hydroxyl and/or amino and/or amido and/or imido groups,-   (b) from 0.5 to 80% by weight, especially from 30 to 75% by weight,    in particular from 45 to 70% by weight, of one or more cetane number    improvers, preferably 2-ethylhexyl nitrate, alone or in a mixture    with other cetane number improvers, preferably 2-ethylhexyl nitrate,    alone or in a mixture with other cetane number improvers, and-   (c) from 0.7 to 20% by weight, especially from 1.1 to 15% by weight,    in particular from 1.5 to 10% by weight, of a mixture of carboxylic    acids (A) and polycyclic hydrocarbon compounds (B) as specified    above.

The examples which follow are intended to further illustrate the presentinvention without restricting it.

EXAMPLES 1A (FOR COMPARISON) AND 1B (INVENTIVE)

The two duel additive concentrates 1A and 1B which are suitable for usein diesel fuel have the compositions specified in Table 1 [in % byweight]:

TABLE 1 1A 1B Detergent * 20.31 27.66 2-Ethylhexyl nitrate as a cetanenumber improver 46.87 63.83 Tall oil fatty acid (fatty acid content: 97%by weight) 0 6.38 2-Ethylhexanol as a diluent 31.25 0 Commercialdefoamer 1.25 1.70 Commercial corrosion inhibitor 0.32 0.43 * Imideformed from polyisobutenyl-substituted succinic anhydride (M_(n) of thepolyisobutenyl radical: 1000) and tetraethylenepentamine

Result of the Storage Experiments:

Concentrate 1A became distinctly cloudy even after 2 weeks of storage at40° C., whereas concentrate 1B remained clear after 50 weeks of storageat 40° C.

1. The method of using mixtures of (A) aliphatic saturated orunsaturated monocarboxylic acids having from 12 to 24 carbon atoms ortheir dimerization or trimerization products, which may be present asfree carboxylic acids and/or in the form of ammonium salts, amides,esters and/or nitrites, and (B) polycyclic hydrocarbon compounds whichcontain carboxyl groups and are obtainable from distillation residues ofnatural oils which have been extracted from tree resins for improvingthe storage stability of fuel additive concentrates which comprise atleast one detergent and at least one cetane number improver, themixtures of components (A) and (B) being used in a concentration of from0.7 to 20% by weight based on the total amount of the fuel additiveconcentrate.
 2. The method according to claim 1, in which the fueladditive concentrates comprise at least one detergent having moietieswhich are derived from succinic anhydride and have hydroxyl and/or aminoand/or amido and/or imido groups.
 3. The method according to claim 2, inwhich the fuel additive concentrates comprise at least onepolyisobutenyl-substituted succinimide as a detergent.
 4. The methodaccording to claim 1, in which the fuel additive concentrates comprise2-ethylhexyl nitrate as the cetane number improver.
 5. The methodaccording to claim 1, in which the carboxylic acids (A) and thepolycyclic hydrocarbon compounds containing carboxyl groups (B) arepresent in the mixture in a weight ratio of from 65:35 to 99.9:0.1, inparticular from 90:10 to 99.9:0.1.
 6. The method according to claim 1,in which the mixture of carboxylic acids (A) and polycyclic hydrocarbonscontaining carboxyl groups (B) used is tall oil fatty acid or dimerizedtall oil fatty acid.
 7. The method according to claim 1, in which themixture of carboxylic acids (A) and polycyclic hydrocarbon compoundscontaining carboxyl group (B) is used in amounts of from 0.7 to 20% byweight, in particular from 1.5 to 10% by weight, based on the totalamount of the fuel additive concentrate.
 8. A fuel additive concentratecomprising, based in each case on the total amount of the fuel additiveconcentrate, (a) from 0.5 to 60% by weight of one or more detergentswhich have moieties which are derived from succinic anhydride and havehydroxyl and/or amino and/or amido and/or imido groups, (b) from 0.5 to80% by weight of one or more cetane number improvers and (c) from 0.7 to20% by weight of a mixture of carboxylic acids (A) and polycyclichydrocarbon compounds containing carboxyl groups (B) according to claim1.